1. Technical Field
The present invention relates to a vehicle steering control system which employs an electric motor or the like to provide an additional front wheel steering angle to a front wheel steering angle operated by a vehicle operator.
2. Related Art
Conventionally, various techniques have been suggested which are employed to correct a front wheel steering angle operated by a vehicle operator. For example, a steering control system is disclosed in Japanese Patent Application Laid-Open No. 2004-168166, which employs variable steering gear ratios. This steering control system is configured to determine the steering gear ratio based on the sum of a proportional term dependent on the steering angle and a differential term dependent on the steering angular speed. The system is also configured to change the differential term from the positive region to the negative region as the vehicle speed is increased.
The conventional steering control system as disclosed in Japanese Patent Application Laid-Open No. 2004-168166 mentioned above is intended to improve actual steering in response to a steering input from the vehicle operator. However, the system is not configured to counteract various situations, which may occur during vehicle operator's maneuvers, to properly maintain the steering angle. For example, the vehicle operator may press the brake pedal fully during cornering, thereby causing a wheel to lock. In such a situation, the vehicle will not be able to travel in the intended cornering direction and thus the vehicle operator may further steer the vehicle. In such a case, the system can not provide proper braking force.